The present invention relates to leak detectors, and, more particularly, to apparatus for detecting leaks occurring in liquid receptacles where the receptacles are not accessible for direct observation.
While not limited thereto, the invention is well suited to and will be described with reference to leak detection from petro chemical tanks. A problem that commonly occurs in places where petro chemicals such as gasoline are stored, e.g., gas stations, is that leaks develop in the tanks and such condition cannot be detected until excessive leakage has occurred. This is due to the fact that liquid level in the tanks varies at a significant rate in response to intentional discharge of gasoline and masks the slow level change due to leakage.
Aside from the old fashioned dip stick or measuring rod there are various known devices for providing readout of tank contents. Capacitive probes have been used as well as floats positioning adjustable potentiometers. However, these devices provide continuous readings that vary as a result of normal pumping at a significantly greater rate than any variation due to leakage. Also, unless successive readings can be taken over an extended period of time without intervening normal discharge of the tank contents, the difference due to a slow leak will be unobservable.
One other type of float actuated liquid-level monitoring device is known wherein the float carries a permanent magnet and successively actuates the individual magnetic reed switches in an array of such switches. The switches are connected to respective taps on a resistance network in a potentiometer-like circuit operative to switch taps along the resistance, stepwise, providing a stepped voltage output when a voltage source is connected across the resistance network. It is perception of a characteristic of this last mentioned type of level monitoring device that has led to the present invention.